It is commonly required in medical fields to secure a probe including an electrode adjacent the surface of a patient's skin for measuring and monitoring purposes. It is also desirable to secure an electrode adjacent the scalp of a fetus or a neonate without such securing causing trauma to the patient, as is conventionally caused by invasion of the fetus or neonate.
FR-A-2569976 discloses a resilient suction member for securing an electrode adjacent the surface of a patient's skin, in which a resilient boss has secured therein a plurality of concentrically mounted electrodes one of which, namely a monitoring pick-up, is exposed on the face of the boss which is applied to the skin. The exposed electrode is surrounded by three concentric, shallow channels formed in the otherwise flat face of the boss. The channels are connected via passageways to a source of sub-atmospheric pressure in the form of a vacuum pump so that, when the face of the boss is applied to the skin, the chamber formed by the channels and the skin may be evacuated with the result that the boss, and hence the electrode, is secured by suction against the skin.
The suction member of FR-A-2569976 suffers the disadvantage that the channels are necessarily small dimensions when the suction member itself is manufactured small enough for application to the scalp of a neonate or a prenatal fetus. Consequently the area of scalp over which the reduced pressure in the channels acts, and hence the downward securing force, is small. This downward force is spread over a multiplicity of upwardly directed supporting rings with the result that the sealing effect of the suction member is small. To overcome the prospect of resulting leakage, the source of sub-atmospheric pressure required to retain the monitoring pick-up in secure contact with the monitored surface, has to be one which can pump out the cavity indefinitely, i.e. a mechanical/electrical pump. Such pumps are costly and bulky. This arrangement may be uncomfortable for the patient, and it is in addition frequently required to supplement the securing action of the suction member with surgical adhesive tape as the suction created in a small suction member is barely sufficient to retain the electrode adjacent the scalp. For these reasons it is believed that this proposed suction member has not achieved practical use, especially in connection with the monitoring of a pre-natal fetus or as an intra-uterine device.
U.S. Pat. No. 4,217,908 and U.S. Pat. No. 4,369,793 disclose medical instrumentation electrode apparatus for use in connecting wiring from an external medical instrument such as an electrocardiograph machine with an area of a patient's skin. The apparatus includes a vacuum bell which is interconnectible with a resilient bulb for partially evacuating the same and causing a pliable ring disposed on the open end of the bell to collapse against a patient's skin. In this manner a disposable contact held in place within the vacuum bell by a core portion of the bell is held in electrical contact with the skin area. The core portion is integrally formed with the vacuum bell and includes an upper protruding end for connection with the resilient bulb and is further provided with an air communicating passage extending between the bulb and the interior of the vacuum bell. A single electric contact is provided for connecting a wire from an electrocardiograph machine to the contact.
WO-A-85/00018 discloses an electrode unit for use in electrotherapy comprising a cup that is collapsible by suction applied to a pipe that forms the stem of an electrode disc within the cup. Conduits communicate the inside of the cup through a boss with the atmosphere through an external groove. A sleeve extends from the boss and has a circumferential rib or flange. The sleeve can be folded back to engage the flange into the groove to block off the conduits which connect to atmosphere to permit the cup to collapse when the rim of the cup is placed against the body of a patient and suction is applied, and the sleeve can be lifted up to admit air into the conduits in order to release the cup.
It will be appreciated that none of the arrangements described in the aforesaid US and International references would be suitable for application to the head of an unborn fetus located in the mother's uterus for monitoring the condition of the fetus.